18Cr-10Niステンレス鋼のMgCl₂溶液中における応力腐食割れ形態の電位依存性

抄録

The effect of the MgCl₂ concentration-potential relationship on the transgranular stress corrosion cracking (TGSCC) and intergranular stress corrosion cracking (IGSCC) of solution treated and sensitized 18Cr-10Ni-0.15C stainless steel was investigated in 15 to 35% MgCl₂ solutions at 80°C under the stress of 25kg/mmmm². The effect of applied stress on SCC mode of sensitized 18Cr-10Ni-0.15C stainless steel was also studied.
Only the TGSCC occurred in the solution treated 18Cr-10Ni-0.15C stainless steel when the concentration of MgCl₂ was above 30%, and the potential range of SCC was widened with an increase of MgCl₂ concentration. The MgCl₂ concentration-potential range for TGSCC or mixed types of SCC of sensitized 18Cr-10Ni-0.15C stainless steel was almost the same with that for TGSCC of the solution treated one. The potential range in which only the IGSCC occurred was just below that of TGSCC in the case of sensitized 18Cr-10Ni-0.15C stainless steel, and this potential range became wider with a decrease of MgCl₂ concentration.
It was found that the fracture shifted from TGSCC to IGSCC with an increase of applied stress in the same environmental condition.
The anodic polarization curves of 6 to 18Cr-10Ni and 18Cr-10Ni-0.15C steels were measured. The mechanisms of TGSCC and IGSCC were also discussed.